BEIJING -- Smog will hit some parts in North and Central China on Saturday, the Ministry of Environmental Protection (MEP) warned, urging local authorities to make plans.

The smog, which will return to Hebei, Shanxi, Shandong and Henan provinces, is expected to last until a cold front comes to the rescue around Thursday, the ministry said.

Authorities in the affected regions were asked to adopt plans to cut emissions and mitigate pollution. The environment ministry will send inspection teams to check implementation of the plans.

Despite government efforts to fight pollution, outbreaks of smog have become increasingly common in winter in northern China where cold weather conditions and the burning of coal for heating combine to exacerbate the situation.

Severe smog triggered red alerts in more than 20 cities at the beginning of the new year. When authorities issue red alerts, some manufacturers are required to cut production, and heavily polluting vehicles are banned from the roads.

In environment inspections last year, the MEP said a total of 720 people were detained and 6,454 held accountable for environment-related wrongdoing.

In 2016, the government refused 11 high-pollution and high-energy consuming projects, involving total investment of 97 billion yuan (about $14 billion).

Partly due to those efforts, Chinese cities reported less PM2.5 pollution in 2016, with the average density of PM2.5 in 338 cities falling by 6 percent.

China is aiming for a 10-percent reduction in air emissions from 2012 levels by 2017 in cities at the prefecture level and above. Meanwhile, the PM 2.5 density in Beijing, Tianjin and Hebei Province should drop 25 percent.